In the early years of oil production it was not uncommon for a blowout on an oil well being drilled to occur. A blowout is an uncontrolled release of oil from an oil well or gas from a gas well. One may think of the classic picture of a gusher at Spindletop, Tex. throwing oil out of the top. Blowouts are both dangerous and wasteful. Blowouts would often push the drill string out of the well and injure or kill workers.
With the advent of rotary drilling techniques, which use the density of the drilling fluid, or “mud,” to overcome the downhole pressure of a penetrated zone, gushers became less frequent. At times, however, the fluid density was not adequate and a blowout would still occur. In the 1920s, blowout preventers (BOP) were developed to regulate the pressure at or near the wellhead and they soon became standard equipment. In recent times, blowout preventers have entered the news because of the alleged failure of the 300-ton blowout preventer on the Deepwater Horizon well off the coast of Louisiana. Three main manufacturers of blowout preventers today are Hydril, Cameron, and Shaffer.
In modern drilling operations, drill strings are placed through a blowout preventer stack before running toward the oil and gas reservoir. The drilling fluid (mud) is pumped through the drill string down to the drill bit and then returns up the space (annulus) between the outside of the drill pipe and the casing. When an excessive influx of pressure enters from the reservoir, automated systems or an operator activates the blowout preventer and the blowout preventer seals the annulus and stops the flow of fluids.
Because blowout preventers are so important to safety and protection of the environment, regulations and practices require that blowout preventers be inspected on a regular basis. For example, after drilling a well, the blowout preventer is typically tested to make sure that there are no leaks. Depending one wear and circumstances, the seals within the blowout preventer are replaced. To replace the seals, the blowout preventer is opened, and in particular the annular BOP head is removed. Conventionally, the studs in the annular head are turned manually using a pipe through the studs on the annular head and with the workers suspended in a basket. The process is more dangerous, difficult, and time consuming than desired.